The present invention relates to a submersible pump system for producing hydrocarbons from gassy wells and a method for protecting the submersible pump of such systems. More particularly, the present invention relates to a system and method in which a submersible pump communicating with the lower end of a production tubing of an oil well completed into a gassy formation is protected from vapor or gas lock by effectively separating and passing the gaseous components of the produced hydrocarbons to the annulus between the production tubing and the casing at a location upstream of the pump. Thus, the fluid entering the pump is substantially limited to the liquid components of the production fluid.
Submersible pumps carried on the lower end of production tubing provide an economically attractive means to produce hydrocarbons under a variety of circumstances. However, such submersible pumps are susceptible to gas lock in environments having a high gas-liquid ratio. Gas lock is a type of pump failure brought on by an influx into the pump of substantially compressible fluids, i.e., the gaseous components of the production fluid. Once seized in gas lock, it may be difficult to circulate the gaseous component out of the pump to resume normal function. At best, this requires cessation of production to cycle the submersible pump. At worst, gas locking can result in failure of the submersible pump system requiring a trip of the production tubing to access the pump system. The trauma of gas lock stresses the components of the submersible pump and contributes to excessive wear and premature failure of both the pump and the motor, especially in combination with the excessive motor temperatures generated during gas locking. It does not take many preventable trips of the production tubing out of well bore to service a submersible pump or motor in order to substantially alter the economic considerations which otherwise favor submersible pump systems over alternatives for a specific application.
In the past, a single-stage gas separator has been deployed upstream of the pump in order to extend the range of submersible pump systems to formations having a gaseous component of the production fluids. While single-stage gas separators are helpful in limited ranges, gas lock continues to be a substantially limiting factor in the deployment of submersible pumps for production from gassy wells.